This invention relates to data transmission systems, and more particularly to a low profile antenna for a data transponder in such systems.
The concept of remote interrogation of data sources has been applied to many types of systems for automating the readout of the data provided by such data sources. One such application involves the automatic readout of information provided by utility meters to expedite customer billing. One such system is disclosed in U.S. Pat. No. 3,705,385 which was issued Dec. 5, 1972 to the assignee of the present application. In the patented system, a two-way radio link is established between a mobile unit, which serves as an interrogate source, and each of several data transponders which are associated with utility meters which are to be read. Each data transponder unit receives coded signals transmitted from the mobile unit and responsively transmits coded reply data signals with represent the meter reading to the mobile unit. The reply data signals are received and decoded at the mobile unit and the reading data obtained is recorded.
In existing systems of this type, the data transponder includes a quarter wave length whip antenna for receiving signals transmitted from the mobile unit and for radiating signals generated by the data transponder back to the mobile vehicle.
The standard quarter wave whip antenna has been used in most automatic readout systems which employ "radio" interrogation, even though its use is objectionable because of its size and its aesthetic appearance. Moreover, its configuration makes it highly susceptible to vandalism. Also, in many cases, optimum transmitting and receiving efficiencies are not achieved because in view of space limitations, and for appearance sake, it may not be possible to use an antenna having the length necessary to achieve a proper impedance match with the data transponder with which it is used.